This invention relates generally to the practice of orthodontics and in particular to a method and apparatus for generating an orthodontic template for placing orthodontic apparatus.
Orthodontics is known to be the practice of manipulating a patient""s teeth to provide better function and appearance. In general, brackets are bonded to a patient""s teeth and coupled together with an arch wire. The combination of the brackets and wire provide a force on the teeth causing them to move. Once the teeth move to a desired location and are held in place for a certain period of time, the body adapts bone and tissue to maintain the teeth in the desired location. To further assist in retaining the teeth in the desired, the patient may be fitted with a retainer.
To achieve tooth movement, orthodontists utilize their expertise to first determine a three-dimensional mental image of the patient""s physical orthodontic structure and a three-dimensional mental image of a desired physical orthodontic structure for the patient, which may be assisted through the use of x-rays and/or models. Based on these mental images, the orthodontist further relies on his or her expertise to place the brackets and/or bands on the teeth and then manually bends (i.e., shape) the arch wire such that a force is asserted on the teeth to reposition the teeth into the desired physical orthodontic structure. As the teeth move towards the desired location, the orthodontist makes continual judgments as to the progress in the treatment, the next step in the treatment (e.g., new bends in the arch wire, repositioning or replacing brackets, is headgear required, etc.) and the success of the previous step.
In general, the orthodontist makes manual adjustments to the arch wire and/or replaces or repositions brackets based on his or her own expert opinion. Unfortunately, in the oral environment, it is impossible for a human being to accurately develop a three-dimensional mental image of an orthodontic structure due to the limitations of human site and the physical structure of a human mouth. In addition, it is humanly impossible to accurately estimate three-dimensional wire bends (with an accuracy within a few degrees and to manually apply such bends to a wire). Further it is humanly impossible to determine an ideal bracket location to achieve the desired orthodontic structure based on mental images. It is also extremely difficult to manually place brackets in the estimated ideal location. Accordingly, orthodontic treatment is an iterative process requiring multiple wire changes, with the type, success, and speed of treatment being very much dependent on the orthodontist""s motor skills and diagnostic expertise. As a result of multiple wire changes, patient discomfort is increased as well as treatment costs. As one would expect, the quality of care varies greatly from orthodontist to orthodontist, as does the time to treat a patient.
As described, the practice of orthodontic is very much an art, relying on the expert opinion and judgment of the orthodontist. In an effort to shift the practice of the orthodontic from an art to a science, many innovations have been developed. For example, U.S. Pat. No. 5,518,397 issued to Andreiko, et. al, provides a method of forming an orthodontic brace. Such a method includes obtaining a model of the teeth of a patient""s mouth and a prescription of desired positioning of such teeth. The contour of the teeth of the patient""s mouth is determined from the model. Calculations of the contour and the desired positioning of the patient""s teeth are then made to determine the geometry (e.g., groves or slots) to be provided. Custom brackets including a special geometry have been created for receiving an arch wire to form an orthodontic brace system. Such geometry is intended to provide for the disposition of the arched wire on the bracket in a progressive curvature of a horizontal plane and a substantially linear configuration in a vertical plane. The geometry of the bracket is altered, (e.g., by cutting groves into the bracket at individual positions and angles and with particular depth) and in accordance with such calculations of the geometry of the patient""s teeth. In such a system, the brackets are customized to provide three-dimensional movement of the teeth once the wire, which has a two-dimensional shape, (i.e., linear shape in the vertical plane and curvature in the horizontal plane) is applied to the brackets.
Unfortunately, the current innovations to change the practice of orthodontics from an art to a science have only made limited progress. This is due to, but not restricted to, the brackets being the focal point for orthodontic manipulation. By having the brackets as the focal point, placement of each bracket on a corresponding tooth is critical. Since each bracket includes a custom sized and positioned wire retaining grove, a misplacement of a bracket by a small amount (e.g., an error vector having a magnitude of a millimeter or less and an angle of a few degrees or less) can cause a different forced system (i.e., magnitude of movement and direction of movement) than the desired force system to be applied to the teeth. As such, the tooth will not be repositioned to the desired location.
In general, there are two methods for applying brackets to teeth: an indirect method and a direct method. For the indirect method, a tooth impression model is created in the patient""s mouth using a hardening material. The tooth impression model is then used to create a model of the teeth. Brackets are then manually placed on, and temporarily bonded to, the model of the teeth. A transfer tray is then fabricated by taking an impression of the model of the teeth with the brackets installed. Once the transfer tray is fabricated, brackets are placed therein and a bonding agent is applied to the bonding pad of each bracket.
Once an orthodontist has a transfer tray with brackets installed, the orthodontist manually positions the tray into the patient""s mouth to place the brackets on the patient""s teeth. Once the orthodontist believes the brackets are positioned properly, (s)he bonds the brackets to the teeth. Unfortunately, this manual process has limited accuracy to due human limitations. As such, it is extremely difficult, if not impossible, for the orthodontist to position all of the brackets in an ideal location with known bonding agent thickness, slot position, etc. or verify such placements.
The direct bonding method is, as the name implies, a method where the brackets are directly bonded to the patient""s teeth without the use of a transfer tray. The direct bonding method is typically less accurate than the indirect bonding method since the entire process is done manually without any mechanical assistance. Furthermore, it is difficult to manually judge the location of brackets during placement.
U.S. Pat. No. 5,368,478 issued to Andreiko, et. al provides an indirect bonding method that forms jigs for custom placement of orthodontic appliances on teeth. In general, the ""478 patent teaches that each orthodontic template is provided with a surface conforming to the contour of the tooth to which they are to be mounted. Another surface of the orthodontic template engages the bracket to hold it in the proper position and orientation for mounting to the tooth and spaced in relation to the contour surface to precisely locate the orthodontic template on the tooth. The orthodontic templates are particularly useful in positioning brackets of custom appliances desired to the individual anatomy of the patient and requiring custom positions of the brackets on the teeth. While the ""478 patent discloses a method for forming a jig, such jig utilization still keeps the bracket as the focal point of the orthodontic treatment. U.S. Pat. Nos. 5,011,405 and 5,542,842 teach indirect bonding approaches, but suffer the same limitations as the ""478 patent.
Therefore, a need exists for a method and apparatus for generating an orthodontic template that assists in the placement of an orthodontic apparatus without the limitations of current jig and transfer tray designs.